It is typical for thermometers and thermal switches to be calibrated using a drywell. Drywells may include a receiver in which a thermometer or thermal switch is inserted. A heating element and temperature sensor are in thermal contact with the receiver such that the temperature within the receiver may be accurately set. The set temperature of the drywell may then be compared to the readout temperature of the thermometer or the switching temperature of a thermal switch to determine its accuracy. In some uses, a reference thermometer is inserted within the receiver along with the thermometer or switch being calibrated, and the readout of the reference thermometer is used for calibration purposes.
It is important in some applications to provide a uniform temperature gradient between the top and the bottom of the receiver such that the temperature actually imposed on the probe is very close to the set temperature of the drywell or the readout temperature of the reference thermometer. In prior systems, two heating elements are used, one near the top of the receiver and another near the bottom. Two temperature sensors, also located near the top and the bottom of the receiver, provide feedback. A controller receives signals from the temperature sensors and drives the heaters such that the temperature sensors indicate the same temperature.
The above-described approach is costly inasmuch as it requires two thermal sensors. The sensors used must be of extremely high quality and sensitivity inasmuch as they are used for calibration of thermometers and thermal switches that are themselves highly accurate. The sensors may need to be accurate over a broad range—from about 20 to over 600 degrees Celsius. Due to the large temperature changes to which the sensors are subject and the need for accuracy, each of the sensors may need to be serviced or replaced during the life of the drywell. The additional sensor further increases expense by requiring additional circuitry and processing power to provide feedback control using the output of the sensor.
In view of the foregoing, it would be an advancement in the art to provide a drywell using a single receiver-mounted thermal sensor without increasing the cost or processing requirements of the drywell.